Interaction of Polyatomic Molecules with free electron lasers

Free-Electron Lasers (FEL) are new Light Sources which are promising to bring a revolution in our understanding of electron and nuclear dynamics inside driven complex molecules$^{[1]}$.
FEL-pulses are orders of magnitude more intense than the pulses provided by conventional synchrotron radiation sources. FELs have short duration and short-wavelength, ranging from XUV pulses of a few eV to hard Xrays of a few thousand eV. These properties cause the laser to boil away the electrons from the inside out, a fascinating aspect of the interaction of matter with FEL-radiation. That is, when molecules interact with FELs, inner-shell electrons are ionized by single-photon absorption, creating an inner-shell hole. As a result, an Auger process takes place with an outer-shell electron dropping to fill in this hole and another outer-shell electron ionizing. Multiple sequential single-photon ionization (SPI) processes and cascades of Auger transitions take place. This fast electronic re-arrangement leads to the formation of exotic forms of matter, that is, novel, far from equilibrium, states with multiple inner-shell holes. It also results in the Coulomb explosion of the nuclei, i.e. break-up of the molecule, on a femtosecond timescale which is slow compared to the attosecond motion of the electrons. {\it Thus, FELs open new horizons for probing and controlling the attosecond motion of inner-shell electrons in processes far from equilibrium paving the way for revealing fundamental processes in chemical reactions, biological molecules and matter under extreme conditions, for instance, deep inside planets. }

We will explore the interplay of Auger and single-photon ionization processes in FEL-driven multi-center molecules.
{\it We will also study a fascinating phenomenon, namely, charge redistribution which takes place once an inner-shell electron ionizes primarily from the site of the heavier atom embedded in small multi-center molecules$^{[10]}$. Moreover, we will investigate how to control and enhance charge redistribution by varying the parameters of the FEL-pulse}. Hence, our studies will be instrumental in controlling electron transfer which is required for efficient exchange, conversion and storage of energy in fuel cells, in molecular scale devices and in long-range charge transport in DNA.

{\it We will investigate how to ``clock" the ionization and the fragmentation dynamics of FEL-driven diatomic molecules$^{[7]}$}.
The time and the inter-nuclear distance when Auger and SPI processes take place determine the kinetic energies of the final highly charged atomic ion fragments. We will explore how to change these times and distances in order to control the percentage contribution of the final atomic ions as well as their kinetic energies by varying the parameters of the FEL-pulse. Thus, our studies will significantly contribute towards controlling chemical reactions with unprecedented temporal resolution, which is a problem at the forefront of laser-matter interactions.